Drilling fluids are used in the drilling of subterranean oil and gas wells. In rotary drilling, drilling fluids, also known as drilling muds, or simply “muds,” are used for cooling and lubricating drill bits, lubricating drill pipes, carrying cuttings and other materials from the hole to the surface, and exerting a hydrostatic pressure against the borehole wall to prevent the flow of fluids from the surrounding formation into the borehole. Drilling fluids can become contaminated by compounds encountered in drilling.
For example, gases commonly encountered in subterranean formations include methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), ammonia (NH3), and hydrogen sulfide (H2S). Some of the gases have negative effects and impose additional costs on drilling operations. For example, H2S is toxic, flammable, and corrosive. H2S collects at ground level, which presents a risk that H2S will accumulate over time. In certain concentrations and over time, CO2 may be corrosive to processing equipment by reacting with steel. Because of the properties of gases encountered in drilling operations, it would be beneficial to have a reliable method of determining the concentration of such gases in a subterranean formation and in drilling fluids used forming and servicing subterranean formations.
H2S, CO2, CO, NH3, and other analytes of interest in production fluids in oil and gas exploration and production can be present in an oil phase, an aqueous phase (e.g., a brine) or even in a gaseous phase. Thus, effective measurement of any such analyte should account for different phases in which the analyte may be present.